KR20070002254A - Membrane electrode assembly for fuel cell, method of preparing the same, and stack for fuel cell comprising the same - Google Patents

Abstract

Provided are a membrane electrode assembly for a fuel cell which is maximized in the efficiency of catalyst and can remove the moisture generated at a cathode, its preparation method, and a stack containing the membrane electrode assembly. The membrane electrode assembly comprises an anode and a cathode which are located so as to face each other; and a polymer electrolyte membrane which is located between the anode and the cathode, wherein at least one of the anode and the cathode contains an electrode substrate and a catalyst layer present between the electrode substrate and the polymer electrolyte membrane, and the catalyst layer comprises a metal catalyst and a cation exchange resin and has an average surface roughness of 0.1-2.5 micrometers.

Description

Membrane-electrode assembly for fuel cell, manufacturing method thereof and stack for fuel cell comprising same {MEMBRANE ELECTRODE ASSEMBLY FOR FUEL CELL, METHOD OF PREPARING THE SAME, AND STACK FOR FUEL CELL COMPRISING THE SAME}

1 is a schematic diagram schematically showing the structure of a fuel cell system of the present invention;

[Industrial use]

The present invention relates to a membrane-electrode assembly for a fuel cell, a method for manufacturing the same, and a stack for a fuel cell including the same. More specifically, the catalyst efficiency can be maximized, and moisture generated from the cathode electrode can be quickly removed during battery operation. The present invention relates to a fuel cell membrane-electrode assembly capable of exhibiting excellent output characteristics, a method for manufacturing the same, and a stack for a fuel cell including the same.

[Prior art]

Fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxidant contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy. And low temperature fuel cells.

Among these, the low-temperature fuel cell is a clean energy source that can replace fossil energy, and has high power density and energy conversion efficiency, can be operated at room temperature, and can be miniaturized and encapsulated so that it can be used in pollution-free cars, household power generation systems, and mobile devices. The polymer electrolyte fuel cell (PEMFC) and the direct oxidation fuel cell (DOFC) which can be widely used in the field of portable power supply of military equipment, military equipment, etc. are mentioned. In particular, when methanol is used as a fuel in a direct oxidation fuel cell, it is called a direct methanol fuel cell (DMFC). DMFC has the advantage of being able to operate at room temperature compared to other types of fuel cells, and can produce a wide range of outputs by stacking unit cells, and has an energy density of 4 to 10 times that of a small lithium battery. It is drawing attention as a new portable power source.

In the fuel cell system as described above, the stack which substantially generates electricity includes several unit cells including a membrane electrode assembly (MEA) and a separator (or a bipolar plate). It has a stacked structure of dozens. The membrane-electrode assembly has a structure in which an anode electrode (also called "fuel electrode" or "oxide electrode") and a cathode electrode (also called "air electrode" or "reduction electrode") are bonded to each other with a polymer electrolyte membrane interposed therebetween. Have

The separator serves as a passage for supplying fuel required for the reaction of the fuel cell to the anode electrode and for supplying an oxidant to the cathode electrode, and a conductor for connecting the anode electrode and the cathode electrode of each membrane-electrode assembly in series. At the same time. In this process, the electrochemical oxidation of the fuel occurs at the anode electrode, the electrochemical reduction of the oxidant occurs at the cathode electrode, and electricity, heat, and water can be obtained together due to the movement of the generated electrons.

The membrane-electrode assembly is composed of a solid polymer electrolyte membrane and a carbon supported catalysts electrode layer. In this case, Nafion (Nafion) is used as the polymer electrolyte membrane that serves as an electrolyte. , Manufactured by DuPont), Premion (Flemion , Manufactured by Asahi Glass, Asiplex , Manufactured by Asahi Chemical) and Dow XUS And perfluorosulfonate ionomer membranes, such as electrolyte membranes manufactured by Dow Chemical Co., Ltd., are widely used, and the carbon-supported catalyst electrode layer is made of porous carbon paper or carbon cloth. The carbon support in which fine catalyst particles, such as platinum (Pt) or ruthenium (Ru), were supported on the electrode support of the present invention was combined with a waterproof binder.

The present invention is to solve the above problems, an object of the present invention is to maximize the catalyst efficiency by controlling the thickness and roughness of the catalyst layer, fuel cells that can quickly remove the moisture generated from the cathode electrode during battery operation To provide a membrane-electrode assembly.

Another object of the present invention is to provide a method for manufacturing the fuel cell membrane-electrode assembly.

Yet another object of the present invention is to provide a stack including the membrane-electrode assembly for fuel cells.

In order to achieve the above object, the present invention includes an anode electrode and a cathode electrode positioned opposite to each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein at least one of the anode electrode and the cathode electrode is an electrode substrate And a catalyst layer positioned between the electrode substrate and the polymer electrolyte membrane, wherein the catalyst layer comprises a metal catalyst and a cation exchange resin and has an average surface roughness (Ra) of 0.1 to 2.5 μm. Provide an electrode assembly.

The present invention also provides a method of manufacturing a membrane-electrode assembly for a fuel cell comprising forming a catalyst layer on a polymer electrolyte membrane using a catalyst layer-forming composition comprising a metal catalyst, a cation exchange resin, a low vapor pressure surfactant and a solvent. to provide.

More preferably, the method for producing a membrane-electrode assembly according to an embodiment of the present invention comprises the steps of preparing a composition for forming a catalyst layer by mixing a metal catalyst, a cation exchange resin, a low vapor pressure surfactant and a solvent, the composition for forming a catalyst layer Coating a surface of a bulk carrier film to form a catalyst layer, transferring the catalyst layer to a polymer electrolyte membrane, acid treating the polymer electrolyte membrane to which the catalyst layer is transferred, and an electrode substrate on the acid-treated polymer electrolyte membrane May comprise the step of binding.

The present invention also provides a stack for a fuel cell including the membrane-electrode assembly and a separator in which a flow channel is formed by supplying gas in contact with the anode electrode and the cathode electrode of the membrane-electrode assembly.

Hereinafter, the present invention will be described in more detail.

Typically, the membrane-electrode assembly is prepared by coating a composition for forming a catalyst layer including a cation exchange resin on an electrolyte membrane or an electrode substrate by spraying, doctor blade coating, screen printing, or the like. In particular, in order to laminate the catalyst layer to the electrolyte membrane by decal transfer, the composition for forming the catalyst layer is coated on a carrier film by screen printing technique to form a three-layer catalyst-coated membrane. ), The volatile components of aliphatic alcohols such as dipropylene glycol or the like are added, or the surfactant is added to homogeneously disperse the composition for forming the catalyst layer and to control the viscosity appropriately to precisely control the thickness of the catalyst layer. do. However, when a surfactant having a high vapor pressure is used, there is a problem in that it is not removed in a low-temperature firing process of 150 ° C. or lower, and remains in the membrane-electrode assembly, thereby causing a decrease in catalytic activity through side reactions.

On the other hand, the present invention by controlling the viscosity of the catalyst slurry using a low vapor pressure surfactant, it is possible to control the thickness and roughness of the catalyst layer, thereby maximizing the catalyst efficiency, and at the cathode Moisture generated could be removed quickly.

That is, the membrane-electrode assembly according to the embodiment of the present invention includes an anode electrode and a cathode electrode located opposite each other; And a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, at least one of the anode electrode and the cathode electrode includes an electrode substrate and a catalyst layer positioned between the electrode substrate and the polymer electrolyte membrane, wherein the catalyst layer is a metal It comprises a catalyst and a cation exchange resin, and has an average surface roughness (Ra) of 0.1 to 2.5 mu m.

More preferably the catalyst layer has an average surface roughness of 0.1 to 1 μm. The roughness of the catalyst layer is preferred because it can maximize the catalyst efficiency within the above range, and beyond the above range, especially when it exceeds 2.5㎛, the electrochemically generated water stagnation can be hindered in the inflow of the reactants Not.

The catalyst layer also includes micropores in the catalyst layer. Preferably, the catalyst layer has a porosity of 1 to 50% by volume relative to the total volume of the catalyst layer, and more preferably has a porosity of 2 to 30% by volume. If the porosity of the catalyst layer is less than 1% by volume, it is not preferable because the inflow of the reactants is not smooth, and if it exceeds 50% by volume, the electrical resistance increases, which is not preferable.

The catalyst layer has a thickness of 5 to 50 μm, more preferably 5 to 30 μm. If the thickness is less than 5 μm, the amount of loading of the catalyst is too low, which may lead to a slow redox reaction rate of the reactants.

The catalyst layer comprises a so-called metal catalyst which catalyzes the related reactions (oxidation of hydrogen and reduction of oxygen), wherein the catalyst layer according to an embodiment of the present invention comprises a metal catalyst and a cation exchange resin, preferably the catalyst layer 50 to 95 parts by weight, more preferably 60 to 90 parts by weight of the metal catalyst, based on 100 parts by weight; And 5 to 50 parts by weight, more preferably 10 to 40 parts by weight of the cation exchange resin. In the above content range, the hydrogen ion conductivity and the electrical conductivity of the catalyst layer are balanced, and if the content is out of the content range, the electrical resistance or the hydrogen ion transfer resistance increases, which is not preferable for the fuel cell application.

Platinum-based metal catalysts may be used as the metal catalyst, and preferably platinum and platinum-M alloys (M = Ru, Os, Ga, Pd, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, At least one selected from the group consisting of W, Sn, Mo, Rh, and Zn), and more preferably Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, One or more selected from the group consisting of Pt / Ru / Rh / Ni and Pt / Ru / Sn / W can be used. Also, in general, those supported on a carrier can be used. As the carrier, carbon such as acetylene black or graphite may be used, or inorganic fine particles such as alumina or silica may be used. In the case of using the noble metal supported on the carrier as a catalyst, a commercially available commercially available product may be used, or the noble metal supported on the carrier may be prepared and used. Since the process of supporting the precious metal on the carrier is well known in the art, detailed descriptions thereof will be readily understood by those skilled in the art even if the detailed description is omitted.

In addition, the cation exchange resin serves as a hydrogen ion transfer and a binder, it may be used one or more selected from the group consisting of fluorine-based and non-fluorine-based cation exchange resin.

As said fluorine-type cation exchange resin, the ion exchange resin which has cation exchange groups, such as a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a phosphonic acid group, these derivatives, can be used for a side chain. It is preferable that the said ion exchange resin has an ion exchange ratio of 3-33. In the present specification, the ion exchange ratio refers to a value defined by the number of carbon and cation exchange groups in the polymer backbone. In addition, this ion exchange ratio is equivalent to about 700 to 2000 equivalent weight in terms of equivalent weight (EW), which is defined as the weight of the acidic polymer required to neutralize one equivalent of base (NaOH). The hydrogen ion conductivity can be adjusted according to the equivalent weight, and if the equivalent weight is too large, the electrical resistance is increased by that amount, while if the equivalent weight is too small, the mechanical properties are deteriorated, so it is preferable to adjust it in an appropriate range.

Examples of the fluorine-based cation exchange resins include perfluoro-based polymers or fluoro ether-based polymers, and specific examples thereof include poly (perfluorosulfonate) represented by Chemical Formula 1 below (trade name Nafion). (Made by EI Dupont), Aciplex (Manufactured by Asahi Kasei Chemical), Flemion (Asahi Glass, Inc.) and Fumion (manufactured by Fumatech Co., Ltd.) and the like, fluorocarbon vinyl ether represented by the following general formula (2) or fluorinated vinyl ether represented by the following general formula (3). Or the polymers described in US Pat. Nos. 4,330,654, 4,358,545, 4,417,969, 4,610,762, 4,433,082 and 5,094,995, 5,596,676 and 4,940,525.

(In Formula 1, X is H, Li, Na, K, Cs or TBA (tetrabutylammonium) or NR1R2R3R4, R1, R2, R3 and R4 are independently H, CH ₃ or C ₂ H ₅ , and m is At least 1, n is 2, x is about 5 to 13.5, and y is at least 1,000.)

MSO ₂ CFRfCF ₂ O [CFYCF ₂ O] _n CF = CF ₂

(In Formula 2, Rf is fluorine or a C ₁ to C ₁₀ perfluoroalkyl radical, Y is a fluorine or trifluoromethyl radical, n is an integer of 1 to 3, M is a fluorine, hydroxyl radical , Amino radicals and -OMe (Me is selected from the group consisting of alkali metal radicals and quaternary ammonium radicals)

(In Formula 3, k is 0 or 1, l is an integer of 3 to 5)

The poly (perfluorosulfonate) represented by Formula 1 has a micellar structure when the sulfonic acid group at the chain end is hydrated, which provides a passage for hydrogen ion migration and exhibits the same behavior as a typical aqueous solution acid.

The non-fluorine cation exchange resin may be benzimidazole-based polymer, polyimide-based polymer, polyetherimide-based polymer, polyphenylene sulfide-based polymer, polysulfone-based polymer, polyethersulfone-based polymer, polyetherketone-based polymer, poly And ether-ether ketone polymers, polyphenylquinoxaline polymers, polyether polymers, polyphenylene oxide compounds or polyphosphazene polymers. Specific examples of the non-fluorine cation exchange resin include polybenzimidazole, polyimide, polysulfone, polysulfone derivative, sulfonated poly (ether ether ketone: s-PEEK), poly Phenylene oxide, polyphenylene sulfide, or polyphosphazene is mentioned.

In addition, the cation exchange resin may be a form in which a polystyrene sulfonic acid polymer is grafted to a monomer such as ethylene, propylene, fluoroethylene, ethylene / tetrafluoroethylene (ETFE), or the like.

In the present invention, the cation exchange resin may be used in the form of a single substance or a mixture, and may also be optionally used with a nonconductive polymer. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use. The non-conductive polymer may be polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene- perfluoroalkyl vinyl ether copolymer (PFA) ethylene / tetrafluoro Copolymers of ethylene (Ethylene / Tetrafluoroethylene (ETFE)), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) It is preferable to use at least one selected from the group consisting of, and more preferably to use poly (perfluorosulfonate).

The electrode substrate serves to support the fuel cell electrode and to diffuse the reaction gas into the catalyst layer to facilitate the access of the reaction gas to the catalyst layer, generally composed of a conductive substrate, such a conductive substrate, carbon paper , Carbon cloth or carbon felt may be used, and more preferably hydrophobized ones may be used.

In addition, the membrane-electrode assembly according to the embodiment of the present invention includes a fine powder containing a conductive powder and a fluorine-based binder resin between the catalyst layer and the electrode substrate in order to facilitate contact between the electrode substrate and the catalyst layer and to uniform gas diffusion. It may further include a microporous layer.

The microporous layer includes micropores having an average pore diameter of 0.01 to 1㎛, more preferably micropores having an average pore diameter of 0.01 to 0.5㎛. If the diameter of the micropores is less than 0.01 μm, it is not preferable for the inflow of the reactants and the discharge of the electrochemically generated moisture.

It is preferable that the microporous layer has a thickness of 0.5 to 100 μm, more preferably 1 to 50 μm. If the thickness of the microporous layer is less than 0.5 μm, pin holes or short circuits between the catalyst layer and the electrode substrate may be caused, which is not preferable. If the thickness of the microporous layer is more than 100 μm, the oxygen diffusion resistance of the cathode electrode may be increased. Not.

The microporous layer includes 50 to 95 parts by weight of conductive powder, more preferably 60 to 95 parts by weight, and 5 to 50 parts by weight of fluorine-based binder resin, and more preferably 5 to 100 parts by weight of microporous layer. It contains 40 parts by weight. Within the content range, the electrical conductivity is low and the inflow and removal of the overreactant is smooth, and if it is out of the content range, the electrical resistance is increased or the mechanical coupling force is not preferable.

Examples of the conductive powder include carbon powder, carbon black, acetylene black, ketjen black, activated carbon, carbon nanotubes, carbon nanofibers, carbon nanowires, and the like. carbon nano rings) can be used. Examples of the fluorine-based binder resin include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and ethylene / tetra With copolymers of ethylene / tetrafluoroethylene (ETFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) It is possible to use one or more selected from the group consisting of, more preferably a polymer solution or dispersion of polytetrafluoroethylene. In the present invention, a PTFE emulsion (manufactured by Aldrich) which suspended solid PTFE polymer particles in deionized water to have a composition of about 60% was used.

Membrane-electrode assembly according to an embodiment of the present invention, a manufacturing method comprising the step of forming a catalyst layer on the polymer electrolyte membrane using a catalyst layer-forming composition comprising a metal catalyst, a cation exchange resin, a low vapor pressure surfactant and a solvent. It can be prepared by.

More preferably, a) preparing a composition for forming a catalyst layer by mixing a metal catalyst, a cation exchange resin, a low vapor pressure surfactant and a solvent; b) coating the catalyst layer forming composition on one surface of a bulk carrier film to form a catalyst layer; c) transferring the catalyst layer to a polymer electrolyte membrane; d) acid treating the polymer electrolyte membrane to which the catalyst layer is transferred; And e) binding an electrode substrate to the acid-treated polymer electrolyte membrane.

Hereinafter, the method of manufacturing the membrane-electrode assembly will be described in more detail. First, a metal catalyst, a cation exchange resin, and a solvent are mixed in a solvent, and a low vapor pressure surfactant is further added to adjust the viscosity of the composition to form a catalyst layer composition. To prepare.

The composition for forming a catalyst layer may include 10 to 35 parts by weight of a metal catalyst, more preferably 15 to 30 parts by weight, based on 100 parts by weight of the composition; 3 to 15 parts by weight, more preferably 5 to 10 parts by weight of cation exchange resin; 0.1 to 50 parts by weight of the low vapor pressure surfactant, more preferably 20 to 40 parts by weight; And 10 to 60 parts by weight of solvent, more preferably 20 to 50 parts by weight. In the case of the content range, the concentration and viscosity of the composition may be controlled to form a catalyst layer having a uniform thickness by a method such as silk screen printing. Not.

At this time, the viscosity of the composition for forming the catalyst layer is preferably 500 to 150000 cps, preferably 700 to 100000 cps. If the viscosity of the composition for forming a catalyst is less than 500 cps, it is difficult to form a coating layer of a predetermined area after printing, and if the viscosity exceeds 150000 cps, printability is reduced.

As the metal catalyst and the cation exchange resin, the same compounds as described above may be used.

The metal catalyst is included in 10 to 35 parts by weight, more preferably 15 to 30 parts by weight based on 100 parts by weight of the composition for forming a catalyst layer. The content of the metal catalyst is preferred because it is excellent in dispersibility within the above range, and if it is out of the above range, sedimentation occurs in the composition, or the economic efficiency is lowered due to excessive use of the catalyst, which is not preferable.

The cation exchange resin may be included in an amount of 3 to 15 parts by weight, more preferably 5 to 10 parts by weight, based on 100 parts by weight of the composition for forming a catalyst layer. If the content of the cation exchange resin in the composition for forming the catalyst layer is less than 3 parts by weight, the hydrogen ion transfer function in the catalyst layer is lowered, which is not preferable. Such a cation exchange resin is preferably used in the form of an aqueous dispersion by dispersing in water or a co-solvent of water and alcohol. In this case, the aqueous dispersion of the cation exchange resin is preferably a solid cation exchange resin dispersed in a concentration of 3 to 30% by weight, more preferably 5 to 20% by weight in the solvent. If the concentration of the solid cation exchange resin is less than 3% by weight, it is not preferable because the concentration of the composition decreases due to the excess solvent, and if it exceeds 30% by weight, the viscosity increases and the printability is not preferable.

The low vapor pressure surfactant acts as a thickener in the composition for forming a catalyst layer to smoothly disperse the catalyst particles and form a catalyst layer by coating, and is removed during the acid treatment of the catalyst layer to convert the catalyst layer into a microporous structure. It provides a pathway for the smooth inflow of and rapid removal of reaction byproducts. As the low vapor pressure surfactant, those having a molecular weight (Mw) of 1,000 or less and a vapor pressure of 1 to 1000 Pa can be used, and more preferably, those having a molecular weight of 500 to 1000 and a vapor pressure of 1 to 600 Pa can be used. When the molecular weight of the low vapor pressure surfactant exceeds 1,000 or the vapor pressure exceeds 1000 Pa, it is not preferable because it does not remove quickly during the acid treatment and remains to inhibit the ion conductivity or the electrical conductivity of the catalyst layer.

The low vapor pressure surfactant usable in the present invention is selected from the group consisting of anionic surfactants, cationic surfactants, nonionic surfactants and zwitterionic surfactants. One or more kinds of things can be used.

The said cationic surfactant can be used individually or in mixture of 1 or more types of quaternary ammonium salts and tertiary amidoamine salts. More specifically, quaternary ammonium salts such as cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, distearyldimethylammonium chloride, disetyldimethylammonium chloride and cocaamidopropyldimethylamine, stearamidopropyldimethylamine, oleic acid Tertiary amidoamine, such as amidopropyl dimethylamine and isostear amido propyl dimethylamine, etc. are mentioned.

In general, the anionic surfactant may be applied to all widely used compounds. In particular, carboxylate compounds such as soap, higher alcohols, higher alkyl ethers, and sulfate ester salts of olefins may be used. The compound, the sulfate compound containing alkylbenzensulfonate, and the phosphate compound which phosphorylated higher alcohol can be mentioned. More specifically, sodium lauryl sulfate (hereinafter referred to as 'SLS'), sodium lauryl ether sulfate (SLES), linear alkylbenzenesulfonate (LAS), monoalkyl phosphate (MAP), acyl ise Thionate (acyl isethionate, SCI), and alkyl glyceryl ether sulfonate (AGES), acyl glutamate, acyl taurate, fatty acid metal salt, and the like. It is better to use SLS, SLES, LAS, or SCI, which are widely used.

The nonionic surfactants include ethoxylated fatty alcohols, ethoxylated fatty acids, ethoxylated alkyl phenols and alkanolamides (patty acid alkanolamides). (alkanolamide (fatty acid alkanolamide), ethoxylated fatty acid alkanolamide, fatty amine oxide, patty amido amine oxide, glyceryl patty acid ester ( glyceryl fatty acid esters, sorbitan, ethoxylated sorbitan esters, alkyl poly glycosides, ethylene / propylene oxide copolymers and At least one selected from the group consisting of ethoxylated-propoxylated fatty alcohols; Available.

As the amphoteric surfactant, alkyl amido propyl betaine, alkyl dimethyl betaine, alkyl ampoacetate, alkyl ampodiacetate, or the like can be used.

Of these, nonionic surfactants may be used as the low vapor pressure surfactant, and more preferably octyl-phenoxy-polyethoxylate (Triton). X-100, manufactured by Aldrich, tetramethyl-decyn-diol; surfynol , Manufactured by AIR PRODUCTS), a fluorinated wetting agent (manufactured by 3M), or mixtures thereof, most preferably tetra-methyl-decine-diol.

The low vapor pressure surfactant is included in an amount of 0.1 to 50 parts by weight, more preferably 20 to 40 parts by weight, based on 100 parts by weight of the composition for forming a catalyst layer. When the content of the low vapor pressure surfactant is within the above range, the viscosity of the composition for forming the catalyst layer is appropriate, and after removal of the catalyst layer on the electrolyte membrane, the removal is preferable. It is also preferred that the low vapor pressure surfactant is subsequently removed by acid treatment. It is not preferable because there is a risk of chemical decomposition in the strong redox atmosphere of the fuel cell when remaining.

In addition, as the solvent, alcohols such as ethanol, isopropyl alcohol, ethyl alcohol, n-propyl alcohol, butyl alcohol, or water may be used, and more preferably, a mixture of water and 2-propanol may be used.

The solvent is contained in 10 to 60 parts by weight, more preferably 20 to 50 parts by weight with respect to 100 parts by weight of the composition for forming a catalyst layer. If the content of the solvent is less than 10 parts by weight, the viscosity is lowered and flowability is increased, and therefore, it is not preferable for coating of a uniform area.

The catalyst layer forming composition further comprises a defoamer; Deflocculants for preventing aggregation, including water-soluble polymers such as polyphosphates, lignosulfonates, quebracho, etc .; And additives such as glycerol. These, like the low vapor pressure surfactants, are all removed during the acid treatment during catalyst layer preparation.

Each component which comprises the said composition for catalyst layer formation is mixed uniformly by the method of mechanical mixing or ultrasonic mixing.

The catalyst layer-forming composition prepared after mixing is coated on one surface of a bulk carrier film and dried to form a catalyst layer.

Examples of the bulk carrier film include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer having a thickness of about 200 mm. (PFA) a non-fluorine-based polymer film, such as ethylene / tetrafluoroethylene (ethylene / tetrafluoroethylene (ETFE)), fluorine-based resin film, or polyimide (Kapton ^®, DuPont Co.), such as polyester (Mylar ^®, DuPont Co.) Can be used.

The coating process is selected from the group consisting of screen printing method, spray coating method, coating method using doctor blade, gravure coating method, dip coating method, silk screen method, painting method and slot die coating method according to the viscosity of the composition. It may be carried out by a method, but is not limited thereto. More preferably, screen printing can be used.

Thereafter, the catalyst layer formed on the bulk carrier film is placed on the polymer electrolyte membrane, and then hot rolled under the conditions of 100 to 250 ° C. and 150 to 500 kgf / cm ² to be transferred to the polymer electrolyte membrane. More preferably, hot rolling may be performed under conditions of 120 to 210 ° C. and 200 to 400 kgf / cm ² . Within the above temperature and pressure range, the catalyst layer is smoothly transferred, and if it is out of the above range, the catalyst layer is not completely transferred or the catalyst layer has an excessively dense structure.

The electrolyte polymer membrane is made of a proton-conducting polymer material, i.e., an ionomer, and is generally a tetrafluoroethylene and fluorovinylether copolymer containing a sulfonic acid group, a defluorinated sulfide polyether ketone, an aryl ketone or Polybenzimidazole and the like may be used, but the present invention is not limited thereto. In general, the polymer membrane has a thickness of 10 to 200㎛. Since the method and conditions for preparing the polymer membrane are well known in the art, detailed descriptions thereof will be omitted.

Thereafter, the polymer electrolyte membrane to which the catalyst layer is transferred is subjected to an acid treatment with sulfuric acid or phosphoric acid for about 1 hour at 80 to 100 ° C. and 1 M aqueous solution, and then washed with 100 ° C. deionized water for 1 hour.

If the above conditions are exceeded, the surfactant component in the catalyst layer may not be completely removed, and there is a risk of chemical decomposition in the strong redox atmosphere of the fuel cell.

After the acid treatment, all organic components including the low vapor pressure surfactant are removed, and only the metal catalyst and cationic polymer resin are present in the catalyst layer. Since the low vapor pressure surfactant is non-conductive, a change occurs in electric resistance before and after acid treatment, and micropores are formed in the catalyst layer, thereby increasing the roughness and porosity of the catalyst layer.

In addition, in order to facilitate the adhesion of the catalyst layer and the electrode substrate, and to facilitate the diffusion of gas, including the micropores in the layer, before the acid treatment step, a conductive powder, a fluorine-based binder resin and a solvent are included on the catalyst layer. Coating the composition for forming a microporous layer, and drying and firing may further comprise forming a microporous layer.

The composition for forming the microporous layer includes 5 to 15 parts by weight of the conductive powder, 1 to 2 parts by weight of the fluorine-based binder resin, and 83 to 94 parts by weight of the solvent based on 100 parts by weight of the composition. Within the above content range, the composition is excellent in dispersibility, and if it is outside the above content range, aggregation of the conductive powder occurs or the viscosity is too high, which is not preferable for coating.

The conductive powder and the fluorine-based binder resin are the same as described above. In addition, the solvent may be one or more selected from the group consisting of deionized water, alcohols and their cosolvents. In the coating, a screen printing method, a spray coating method or a coating method using a doctor blade, a gravure coating method, a dip coating method, a silk screen method or a coating method such as a painting method may be used, but is not limited thereto.

As described above, the microporous layer includes micropores having an average pore diameter of 0.01 to 1 μm, and more preferably micropores having an average pore diameter of 0.01 to 0.5 μm. If the diameter of the micropores is less than 0.01, it is not preferable for the inflow of the reactants and the discharge of the electrochemically generated moisture, and if it exceeds 1 μm, brittleness is increased, which is not preferable.

Thereafter, an electrode substrate is bound to the acid-treated polymer electrolyte membrane to prepare a membrane-electrode assembly.

The electrode base material is the same as described above, and the method of binding the electrode base material to the polymer electrolyte membrane is well known in the art, and thus detailed description thereof will be omitted.

The membrane-electrode assembly according to the embodiment of the present invention is easy to maintain the viscosity during mixing by adjusting the viscosity of the catalyst-forming composition with deionized water and a low vapor pressure surfactant instead of volatile components of aliphatic alcohols, in particular the surfactant component is an electrolyte The catalyst layer is removed after being transferred onto the membrane to form micropores in the catalyst layer, thereby reducing the inflow resistance of the reactants and rapidly removing moisture generated at the cathode electrode as a reaction byproduct. Therefore, the membrane-electrode assembly according to the embodiment of the present invention can be applied to both low temperature humidification type, low temperature no humidification type, and high temperature no humidification type fuel cell.

The present invention also provides a stack for a fuel cell comprising the membrane-electrode assembly. Specifically, the fuel cell stack includes the membrane-electrode assembly; And the separator for supplying a gas to the anode electrode and the cathode electrode of the membrane electrode assembly.

In addition, it is possible to provide a fuel cell system comprising the membrane-electrode assembly of the present invention. The fuel cell system includes at least one electricity generator, a fuel supply and an oxidant supply.

The electricity generating unit includes a membrane-electrode assembly including a polymer electrolyte membrane and a cathode electrode and an anode electrode existing on both sides of the polymer electrolyte membrane; And a separator, and serves to generate electricity through an electrochemical reaction between the fuel and the oxidant. The fuel supply unit serves to supply fuel to the electricity generation unit, and the oxidant supply unit serves to supply an oxidant to the electricity generation unit. In the present invention, the fuel is preferably hydrogen, and the oxidant is preferably oxygen or air.

A schematic structure of the fuel cell system of the present invention is shown in FIG. 1, which will be described in more detail with reference to the following.

The fuel cell system 100 of the present invention includes a stack 7 having at least one electric generator 19 for generating electrical energy through an electrochemical reaction between a fuel and an oxidant, and a fuel supply source for supplying the fuel. (1) and an oxidant supply source 5 for supplying an oxidant to the electricity generating unit 19.

In addition, the fuel supply source 1 for supplying the fuel includes a fuel tank 9 for storing fuel, and may further optionally include a fuel pump 11 connected to the fuel tank 9. The fuel pump 11 serves to discharge the fuel stored in the fuel tank 9 by a predetermined pumping force. The oxidant source 5 for supplying the oxidant to the electricity generator 19 of the stack 7 may also be provided with at least one air pump 13 which optionally sucks air with a predetermined pumping force. The electricity generating unit 19 is a membrane-electrode assembly 21 which oxidizes / reduces reaction of hydrogen gas as fuel and oxygen or air in the air, and oxygen gas as oxidant and hydrogen gas as fuel on both sides of the membrane-electrode assembly. It consists of the separators 23 and 25 for supplying the air containing it.

Hereinafter, preferred embodiments of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

(Example 1)

PT Black (Hispec 1000, manufactured by Johnson Matthey) and Pt / Ru Black (Hispec 6000, Johnson Matthey) 4.0g of deionized water was added dropwise to 3.0g of catalyst, respectively, and the catalyst particles were wetted with water. 10 wt% Nafion to the catalyst , Dupont) 9.0g aqueous dispersion was added dropwise and stirred mechanically, 1.0 g TBAOH / methanol solution, sulfinol , Manufactured by AIR PRODUCTS) 0.05g and 4.0g of dipropylene glycol were added, and mechanical stirring and ultrasonic stirring were repeated three times at 30 minute intervals, followed by mechanical stirring using a magnetic stirrer for 12 hours to prepare a composition for forming a catalyst layer. It was.

The composition for forming the catalyst layer was coated with an area of 5 × ⁵ cm ² and a thickness of 50 mm on a Teflon film having a thickness of 250 mm using a 150 mesh stainless steel mask. After drying the catalyst layer-coated Teflon film for 6 hours in an 80 ° C. drying furnace in a nitrogen atmosphere, the solvent was evaporated, the catalyst layers were aligned on both sides of the polymer electrolyte membrane of sodium-form Nafion 115, and then 200 ° C. The catalyst layer was transferred to the polymer electrolyte membrane by applying a temperature and a pressure of 250 kgf / cm ² .

Separately, 3.0 g of carbon black (Vulcan XC-72, manufactured by Cabot) particles contained 9 g of deionized water, 20 g of Triton X-100, 1.0 g of 60% PTFE emulsion, and 0.1 g of surfactant (EviroGEM). AD01, manufactured by Airproduct) was repeated 6 times mechanical stirring and ultrasonic stirring at 1 hour intervals to prepare a composition for forming a microporous layer, and the composition was coated on the catalyst layer transferred to an electrolyte membrane with a thickness of 3 mm.

Finally, the polymer electrolyte membrane in which the catalyst layer and the microporous layer were formed was treated for 1 hour in a 1 M sulfuric acid solution at 100 ° C., and the organic components of the catalyst layer were extracted while converting the Nafion of the catalyst layer and the electrolyte membrane into a proton-form. Finally, the sulfated polymer electrolyte membrane was washed in deionized water at 100 ° C. for 1 hour. The platinum catalyst loadings of the anode electrode and the cathode electrode were adjusted to 4 mg / cm ² , respectively.

The membrane-electrode assembly was physically bonded to E-Tek's catalyst layer-free ELAT gas diffusion body having only a microporous layer formed on one surface of TGPH090 carbon paper treated with 10% water repellency as an electrode substrate, and between two gaskets. After inserting into the two separators in which a gas channel channel and a cooling channel of a certain shape are formed, it was pressed between the copper end plates to prepare a unit cell.

(Example 2)

A unit cell was manufactured in the same manner as in Example 1, except that 5/5 co-solvent of deionized water / 2-propanol was used instead of deionized water when preparing the composition for forming a catalyst layer.

(Comparative Example 1)

A composition for forming a catalyst layer in which an equal weight of proton-form Nafion was impregnated per unit area but using a co-solvent of 1/9 of deionized water / 2-propanol was used. Coated with E-Tek Co., Ltd., a catalyst layer-free ELAT gas diffuser having a layer formed in the same catalyst amount as in Example 1, dried, and thermally compressed at 130 ° C. and 200 kgf / cm ² for 3 minutes on a Nafion 115 electrolyte membrane. A unit cell was prepared in the same manner as in Example 1 except that the membrane-electrode assembly was manufactured without treatment and washing.

(Comparative Example 2)

Except that E-Tek's catalyst layer-containing ELAT gas diffuser impregnated with Nafion having the same weight per unit area was thermocompressed on a Nafion 115 electrolyte membrane under the same conditions as in Comparative Example 1 to prepare a membrane-electrode assembly. In the same manner as in 1, a unit cell was prepared.

For each of the unit cells prepared in Examples and Comparative Examples, 1M methanol and dry air were supplied and operated at a temperature of 70 ° C. for 10 hours, and the operating voltage was measured. The results are shown in Table 1 below.

Evaluation item Example 1 Example 2 Comparative Example 1 Comparative Example 2 Operating voltage at 200 mA / cm ² (V) 0.48 0.45 0.35 0.37

As shown in Table 1, it can be seen that the fuel cells of Examples 1 and 2 manufactured according to the present invention exhibited high output voltages as compared with Comparative Examples 1 and 2 under the same operating conditions.

The membrane-electrode assembly of the present invention can maximize the catalyst efficiency, can quickly remove the moisture generated from the cathode during battery operation, it can exhibit excellent output characteristics.

Claims (24)

An anode electrode and a cathode electrode located opposite each other; And It includes a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, At least one of the anode electrode and the cathode electrode includes an electrode substrate, and a catalyst layer located between the electrode substrate and the polymer electrolyte membrane, The catalyst layer comprises a metal catalyst and a cation exchange resin, the membrane-electrode assembly for a fuel cell having an average surface roughness of 0.1 to 2.5㎛. The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly having a porosity of 1 to 50% by volume relative to the total volume of the catalyst layer. The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly having a thickness of 5 to 50㎛. The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly comprising 50 to 95 parts by weight of the metal catalyst and 5 to 50 parts by weight of the cation exchange resin with respect to 100 parts by weight of the catalyst layer. The method of claim 1, The metal catalyst is platinum, platinum-M alloy (M = Ru, Os, Ga, Pd, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, W, Sn, Mo, Rh and Zn from the group consisting of At least one metal selected) and at least one selected from the group consisting of these metals supported on a carrier. The method of claim 1, Wherein the cation exchange resin is at least one member selected from the group consisting of fluorine-based, non-fluorine-based and hydrocarbon-based cation exchange resin membrane-electrode assembly for fuel cells. The method of claim 6, Wherein the fluorine-based cation exchange resin is a membrane-electrode assembly for a fuel cell having a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. The method of claim 1, The membrane-electrode assembly is positioned between the electrode substrate and the catalyst layer, further comprising a microporous layer comprising a conductive powder and a fluorine-based binder resin. The method of claim 8, The microporous layer is a fuel cell membrane-electrode assembly comprising micropores having an average pore diameter of 0.01 to 1㎛. The method of claim 8, The microporous layer is a fuel cell membrane-electrode assembly having a thickness of 0.5 to 100㎛. The method of claim 8, The microporous layer is a fuel cell membrane-electrode assembly comprising 50 to 95 parts by weight of conductive powder and 5 to 50 parts by weight of a fluorine-based binder resin based on 100 parts by weight of the microporous layer. The method of claim 8, The conductive powder is at least one fuel selected from the group consisting of carbon powder, carbon black, acetylene black, ketjen black, activated carbon, carbon nanotube, carbon nanofiber, carbon nanowire, carbon nanohorn and carbon nano ring Membrane-electrode assembly for batteries. The method of claim 8, The fluorine-based binder resin may be polytetrafluoroethylene, tetra fluoroethylene-hexafluoropropylene copolymer, tetra fluoroethylene-perfluoro alkyl vinyl ether copolymer, ethylene / tetrafluoroethylene, chlorotrifluoroethylene- A membrane-electrode assembly for a fuel cell, wherein the fuel cell is at least one selected from the group consisting of ethylene copolymers, polyvinylidene fluorides, and copolymers of polyvinylidene fluoride-hexafluoropropylene. A method of manufacturing a membrane-electrode assembly for a fuel cell, comprising forming a catalyst layer on a polymer electrolyte membrane using a catalyst layer-forming composition comprising a metal catalyst, a cation exchange resin, a low vapor pressure surfactant, and a solvent. The method of claim 14, wherein the manufacturing method a) mixing a metal catalyst, a cation exchange resin, a low vapor pressure surfactant, and a solvent to prepare a composition for forming a catalyst layer; b) coating the catalyst layer forming composition on one surface of a bulk carrier film to form a catalyst layer; c) transferring the catalyst layer to a polymer electrolyte membrane; d) acid treating the polymer electrolyte membrane to which the catalyst layer is transferred; And e) binding an electrode substrate to the acid treated polymer electrolyte membrane; Method for producing a membrane-electrode assembly for a fuel cell comprising a. The method of claim 14, The composition for forming a catalyst layer comprises 10 to 35 parts by weight of a metal catalyst, 3 to 15 parts by weight of a cation exchange resin, 0.1 to 50 parts by weight of a low vapor pressure surfactant, and 10 to 60 parts by weight of a solvent based on 100 parts by weight of the composition. Method of manufacturing a membrane-electrode assembly for a fuel cell. The method of claim 14, The catalyst layer forming composition is a method of manufacturing a membrane-electrode assembly for a fuel cell having a viscosity of 500 to 150000 cps. The method of claim 14, The low vapor pressure surfactant has a molecular weight (Mw) of 1,000 or less and a vapor pressure of 1 to 1000 Pa of the fuel cell membrane electrode assembly manufacturing method. The method of claim 14, The low vapor pressure surfactant is at least one selected from the group consisting of cationic surfactants, anionic surfactants, nonionic surfactants and amphoteric ionic surfactants, the method for producing a fuel cell membrane electrode assembly. The method of claim 15, The bulk carrier film may be a polytetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, a fluorine resin film including ethylene / tetrafluoroethylene, and Method of producing a membrane-electrode assembly for a fuel cell that is selected from the group consisting of a polymer film containing polyimide or polyester. The method of claim 15, The catalyst layer forming composition is coated on the bulk carrier film by a method selected from the group consisting of screen printing method, spray coating method or coating method using a doctor blade, gravure coating method, dip coating method, silk screen method and painting method Method of manufacturing a membrane-electrode assembly for phosphorus fuel cells. The method of claim 15, Wherein the transfer is carried out by hot rolling under the conditions of 100 to 250 ℃ and 150 to 500 kgf / cm ² Method for producing a membrane-electrode assembly for a fuel cell. The method of claim 15, Before the acid treatment step of the polymer electrolyte membrane, a method for producing a membrane-electrode assembly further comprising the step of forming a microporous layer comprising a conductive powder and a fluorine-based binder resin on the catalyst layer. A membrane-electrode assembly according to any one of claims 1 to 13; And A separator in which a flow channel is formed while supplying gas by contacting an anode electrode and a cathode electrode of the membrane electrode assembly. Stack for a fuel cell comprising a.

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